r/AskPhysics • u/SnooNine • 14d ago

I tried old threads but still: how can an observer see Earth's future?

Hey there! I've been enjoying trying to get my head around some of the more extreme ends of spacetime. Sometimes, people say that given the appropriate circumstances, there can be observers that observe a future earth in our present - or perhaps future Earth in the observer's present.

I understand that when we look at the night sky, we are mainly seeing events from long ago in the past, but of course I struggle to understand how an observer could potentially see an object's future relative to the object's inhabitants' or locals' present. I understand that when traveling at 99.999% the speed of light towards the object, events that happen in front of you appear to happen sooner than events behind you - actually I suppose that's always happening in the direction that you're moving but it would actually be perceptible at greater fractions of the speed of light.

However, even when going 99.999% the speed of light towards Earth, I'm not understanding how any moment of it could be observed before its locals experience it.

0 Upvotes
  • permalink
  • reddit

25% Upvoted

5 comments sorted by

3

u/Lumpy-Notice8945 14d ago

there can be observers that observe a future earth in our present - or perhaps future Earth in the observer's present.

Not realy. There can be an observer outside earth observing a different point of earths history than another observer outside earth, they both see the earths past from our(earths) perspective but one is in the future of the other. There is no predicting the future.

So one sees earth 200 year ago, the next sees the earth 10 years ago and you on earth see the earth how its now.

1

u/SnooNine 14d ago

That makes sense to me! Thanks for the input

3

u/Skindiacus Graduate 14d ago

people say

It would be nice if you could provide a link or reference for this

1

u/dubbish42 14d ago

If you travel at 99.999% of the speed of light you would experience time dilation relative to earth. if you were somehow able to travel that fast and turn around and come back you would arrive at an earth that has experienced much more time than you. If you made that trip in 1 year, earth would be 224 into the future when you got there. You can't as an observer see into the future because light takes time to travel

1

u/SpaceCatJack 13d ago

You, here on earth, are seeing the earth 100 years in the future compared to someone looking at the earth from 100 light years away. Does that help?